Blot the fresh orange collar stain with ammonia and an old washcloth. If the stain has set, blot it with white distilled vinegar. Rinse the white shirt with clean water.
Apply a baking soda paste that contains 4 tbsp. of baking soda and 1/4 cup of warm water if the collar stain remains. Rub the paste onto the orange stain and let it sit for two to three hours. Rinse the baking soda paste off the shirt with clean water.
Apply a laundry pretreatment product to the orange stain before placing it in the washing machine. Follow the directions on the product before you apply it.
Wash the white shirt using the hottest water setting possible. Read the care label on the shirt to determine what water setting to use.
Remove the shirt from the washing machine. Hang the shirt to dry. Repeat the stain removal process until you remove the stain successfully.